In order to enhance the heat transfer performance, the inside wall of a cylindrical heat pipe and/or a screen mesh were coated with a nanoparticle layer. The materials of heat pipe and screen mesh were copper and brass, respectively, and the material of nanoparticles was silicone-dioxide. When the screen mesh was coated with the nanoparticle layer, the thermal resistance increased 2-8% in comparison with the ordinary heat pipe without nanoparticle layer. Clogging of screen mesh with nanoparticles was considered as the main reason of the deterioration of heat transfer performance. On the other hand, when the inside wall of the heat pipe was coated, the thermal resistance was reduced up to 32%. Similar heat transfer performance was achieved even when the screen mesh was removed. This indicates that the nanoparticle layer coated on the inside wall of heat pipe worked as a high performance wick. Since the nanoparticle layer is thin, it may effectively be applied particularly to small heat pipes for small electronic devices.